Diet's Impact On Cancer May Be Major for Some Patients

SAN ANTONIO, Dec. 16 -- The first experiment to show that low-fat diets could help prevent a return of breast cancer now reveals, after a follow-up, that the benefit is almost exclusively for women whose tumor growth was not driven by hormones.

The significance of the new finding could be huge. The finding suggests but cannot prove that these women might be able to cut their risk of dying by up to 66 percent with such diets.

"That's as great or better than any treatment intervention that we've given" for this type of cancer, which is notoriously hard to treat, said C. Kent Osborne of Baylor College of Medicine in Houston, who had no role in the study.

However, for women whose cancers are fueled by hormones -- the vast majority of breast cancer patients -- the diet change seems to make little difference in the risk of recurrence or the chance of survival. Questions remain about whether those who benefited were helped by the reduction in fat or by the weight loss that resulted.

"Maybe it raises as many issues as it answers," said John Milner, chief of nutritional science research at the National Cancer Institute, which paid for the first phase of the study.

Initial results from the study were reported at a cancer conference in 2005 and will appear in this week's Journal of the National Cancer Institute. Results from the longer follow-up on many of the original participants were presented Saturday at the San Antonio Breast Cancer Symposium.

The mixed results were a surprise because doctors had expected all women to benefit, said Rowan Chlebowski of the University of California at Los Angeles, who led the work.

Hormones might play such a strong role in some cancers that dietary changes have only a weak impact on future risk, experts said.

Some earlier studies did not find that low-fat diets reduced the risk of breast cancer. The new one's conclusion that some may benefit from a substantial cut in fat "suggests that getting below a certain threshold of fat intake may be important," said JoAnn Manson, a women's health expert at the Harvard-affiliated Brigham and Women's Hospital.